1. Field of the Invention
This invention relates to an improved offshore platform base. More particularly, this invention relates to an improved structural bulkhead configuration for the base of an offshore platform.
2. Description of the Prior Art
As the exploration and production of petroleum and natural gas extends into deeper waters and more remote locations, a need exists for improved offshore platforms capable of withstanding severe environmental conditions.
Typically, once the exploration of an offshore oil or gas well is completed, a production platform is installed which is either fixed to the ocean floor by piles or rests on the ocean floor. With respect to the latter type of platform (also referred to herein as a gravity structure), the structural integrity of the base portion of the platform is critical to its overall stability. This is particularly the case in an arctic environment because continuously moving ice masses pose a serious threat to the operation of the platform. Even in an ice-free area, wave and current loads, particularly during storms, can be very significant.
A number of base configurations for offshore structures have been developed. Three such configurations include radial-oriented bulkheads, circular-oriented bulkheads and rectangular-oriented bulkheads. U.S. Pat. Nos. 4,045,968 and 4,303,352 illustrate the radial-oriented design. U.S. Pat. Nos. 3,879,952; 3,911,687; 3,961,489; 4,188,157; and 4,304,506 show the circular-oriented bulkheads. U.S. Pat. No. 3,886,753 shows a rectangular-oriented bulkhead configuration. However, each of these configurations have certain disadvantages in view of the many factors which must be considered in designing a new configuration.
Primarily, the structural bulkheads must be capable of withstanding the lateral and vertical loads which will be exerted on the platform. As mentioned above, these loads are significant, particularly in an arctic environment. In addition, the base configuration must be capable of withstanding installation loads. The base must also be able to resist hogging and sagging moments and torsion or twisting during transportation to the final location. Hogging is the straining of a vessel such that the bow and stern are lower than the midship line. Sagging is when the midship line is lower than the bow and stern.
Since the base is typically floated to location, weight is a critical factor. The base for a gravity structure must be capable of retaining various types of ballast materials and, similarly, capable of withstanding loads associated with these ballast materials, particularly the differential pressures between the ballast and the hydrostatic loads, and conditions where no ballast is present.
Industry recognizes a need for an improved base design which will maximize structural integrity both from an installation and an operational standpoint yet minimize weight for transportation and cost reasons.